Quickly calculate reciprocal of large numbers in JavaScript?

Is it quicker to do:

const reciprocal = denominator => 1.0/denominator

Or

const reciprocal = denominator => Math.pow(denominator, -1) //or denominator**(-1)?

Or some other trick?

The denominator is a large (~1e50) integer (in fact it's a factorial) and I need to do lots of similar calculations (roughly 6e5 times).